Culture dependent and independent analysis of bacterial communities associated with commercial salad leaf vegetables

BMC Microbiology

Heather L Tyler¹  Shelly L Osborn¹  Kevin C Randolph¹  Colin R Jackson¹ 

[1] Department of Biology, The University of Mississippi, University 38677, USA

关键词: Pyrosequencing;    Food-borne bacteria;    Salad produce;    Bacterial endophytes;   

Others  :  1142502
DOI  :  10.1186/1471-2180-13-274

 received in 2013-08-22, accepted in 2013-11-26,  发布年份 2013

【 摘 要 】

Background

Plants harbor a diverse bacterial community, both as epiphytes on the plant surface and as endophytes within plant tissue. While some plant-associated bacteria act as plant pathogens or promote plant growth, others may be human pathogens. The aim of the current study was to determine the bacterial community composition of organic and conventionally grown leafy salad vegetables at the point of consumption using both culture-dependent and culture-independent methods.

Results

Total culturable bacteria on salad vegetables ranged from 8.0 × 10³ to 5.5 × 10⁸ CFU g^-1. The number of culturable endophytic bacteria from surface sterilized plants was significantly lower, ranging from 2.2 × 10³ to 5.8 × 10⁵ CFU g^-1. Cultured isolates belonged to six major bacterial phyla, and included representatives of Pseudomonas, Pantoea, Chryseobacterium, and Flavobacterium. Eleven different phyla and subphyla were identified by culture-independent pyrosequencing, with Gammaproteobacteria, Betaproteobacteria, and Bacteroidetes being the most dominant lineages. Other bacterial lineages identified (e.g. Firmicutes, Alphaproteobacteria, Acidobacteria, and Actinobacteria) typically represented less than 1% of sequences obtained. At the genus level, sequences classified as Pseudomonas were identified in all samples and this was often the most prevalent genus. Ralstonia sequences made up a greater portion of the community in surface sterilized than non-surface sterilized samples, indicating that it was largely endophytic, while Acinetobacter sequences appeared to be primarily associated with the leaf surface. Analysis of molecular variance indicated there were no significant differences in bacterial community composition between organic versus conventionally grown, or surface-sterilized versus non-sterilized leaf vegetables. While culture-independent pyrosequencing identified significantly more bacterial taxa, the dominant taxa from pyrosequence data were also detected by traditional culture-dependent methods.

Conclusions

The use of pyrosequencing allowed for the identification of low abundance bacteria in leaf salad vegetables not detected by culture-dependent methods. The presence of a range of bacterial populations as endophytes presents an interesting phenomenon as these microorganisms cannot be removed by washing and are thus ingested during salad consumption.

【 授权许可】

   
2013 Jackson et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

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